1. Field of the Invention
The present invention relates to a method for detecting or assaying a target substance by utilizing an oxygen electrode; more specifically, the invention relates to a method for detecting or assaying a target substance by utilizing specific binding, for example, between an antigen and an antibody or between a receptor and a ligand, the method comprising measuring the activity of a redox catalyst with which one of the antigen and the antibody or one of the receptor and the ligand has been labeled, by means of an oxygen electrode.
2. Description of the Related Art
Various methods for assaying each member in a pair of members specifically binding together (hereinafter referred to as a specific binding pair) have been known, wherein each member includes, for example, an antigen and an antibody in an antigen/antibody pair, and a receptor and a ligand for the receptor in a receptor/ligand pair. It is common to these methods in which one member of such specific binding pair is assayed as target substance A, that the presence or absence of the target substance A or the amount thereof can be determined by allowing the presence or absence of the target substance A or the amount thereof to be reflected as the binding amount of a labeled substance subjected to the specific binding and by detecting or assaying the presence or absence of the labeled substance bound or not bound or the amount thereof.
Various labels including enzyme labels, chemiluminescent labels, fluorescent labels, and radioactive labels, are used as the label. A method has been known for detecting or assaying redox reaction with a redox enzyme, for example, glucose oxidase as such enzyme label on the basis of chromogenic reaction or by means of an oxygen electrode. JP-A-5-72173 discloses a process of detecting an antigen or antibody in an antigen/antibody reaction solution under agitation while putting the antigen/antibody reaction solution into contact with an electrode. The process is disadvantageous, however, in that an enormous volume of such reaction solution is needed and should be agitated for detecting an antigen or antibody, which enforces laborious works and takes a long time, and additionally in that the process cannot be carried out readily at low cost in a simple manner by using a domestic disposable apparatus.
It is an object of the invention to provide a method for detecting or assaying a substance in body fluids, for example, urine and saliva, readily at low cost in a simple manner at home, wherein the substance can function as an indicator of various diseases; and an apparatus to which the method is applicable, for example, a domestic disposable apparatus.
In accordance with the invention, a method for detecting or assaying target substance A capable of specifically binding to specific substance B, by utilizing specific binding between the target substance A and the specific substance B and the reaction of a labeling catalyst is provided, the method comprising allowing a substrate of a redox catalyst to react with the redox catalyst of the target substance A, the specific substance B, third substance Bxe2x80x2 capable of specifically binding to the target substance A, or third substance Axe2x80x2 capable of specifically binding to the specific substance B, in a porous support in contact with the sensing surface of an oxygen electrode, said substances B, Bxe2x80x2 and Axe2x80x2 reflecting the amount of the target substance A, and said substances A, B, Bxe2x80x2 and Axe2x80x2 having been directly labeled with the redox catalyst or bound to a substance labeled with the redox catalyst.
In accordance with the invention, the target substance A, the specific substance B, the third substance Bxe2x80x2 or the third substance Axe2x80x2 is detected or assayed by using an oxygen electrode in contact with a porous support, where a redox catalyst with which the target substance A, the specific substance B, the third substance Bxe2x80x2 or the third substance Axe2x80x2 is labeled, reacts with a substrate of the redox catalyst. Thus, the area of the sensing surface of the oxygen electrode or the depth of the reaction solution in the porous support can be made extremely small; and additionally, an open system can be used because the target substance A can be assayed in such a speedy manner. Therefore, a simple and inexpensive apparatus of small type can be constructed, including for example a domestic disposable apparatus.
The above and other objects, features and advantages of the present invention will become more apparent from the following description.